The invention lies in the field of appliances. The invention relates to a cooktop having a cooktop panel, in particular, made of glass ceramic material, of which the underside has at least one heating element for heating a cooking vessel that can be set down on the cooktop panel. The cooktop has a detection unit that detects the deformation of the cooktop panel as a result of the weight-induced loading by the cooking vessel and determines the corresponding weight-induced loading.
Such a cooktop is disclosed in International PCT publication WO 95/35483. That cooktop has an uninterrupted surface panel with at least one heatable cooking point and a frame. The frame can be supported on a stationary or transportable support, for example, a conventional work top with cooktop cutout. The at least one sensor is disposed on the surface panel, between the surface panel and the frame or between the frame and the support. The at least one sensor is preferably a pressure or force sensor or a displacement sensor combined with a deformable bearing part, the sensor being disposed between the surface panel and the frame or between the frame and the support. Alternatively, it is also possible for the at least one sensor to be a deformation sensor and to be fitted on the surface panel itself, in particular, on the underside of the latter in the border region of the surface panel. The disadvantage of such a configuration of the deformation sensor is the low level of deformation of the cooktop panel by the dead weight of the set-down cooking vessel. The problem with the configuration of a pressure or force sensor in the region of the frame is that forces applied to the frame or the work top during the weighing operation, for example, by the user accidentally supporting himself/herself thereon, act as not inconsiderable and non-correctable disturbance variables. It is also problematic that the cooktop is to have a particularly high level of sealing against penetrating liquids precisely in the region between the cooktop panel and the frame and/or the work top.
U.S. Pat. No. 4,476,946 to Smith also discloses a cooktop. Therein, a circular cooking plate is movably secured in a corresponding opening of a cooktop panel. Fastened on the underside of the cooktop panel is a bending-bar configuration on which the circular cooking plate rests. The dead weight of the cooking plate results in a deflection of the bending bar. The deflection is detected by conventional strain gauges in a bridge-circuit configuration. The weight-induced loading of the cooking plate with a cooking vessel, for example, a pot, set down thereon is detected correspondingly. The disadvantage in the Smith device is the constant permanent loading of the bending bar and, in particular, the problematic sealing behavior in the encircling gap between the cooking plate and the cooktop panel with circular cutouts.
It is accordingly an object of the invention to provide a cooktop with weighing unit that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that, along with the straightforward construction, has sufficient accuracy for the weighing function.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a cooktop including a cooktop panel, at least one heating element for heating a cooking vessel placed upon the cooktop panel, and a weighing unit for detecting a deformation of the cooktop panel as a result of weight-induced loading by the cooking vessel and for determining the corresponding weight-induced loading. The weighing unit is disposed at the underside of the cooktop panel and has an actuating element connected to the cooktop panel and a displacement sensor connected to the actuating element and the cooktop panel. The displacement sensor determines the weight-induced loading from an amount that the actuating element is displaced relative to the displacement sensor as a result of the deformation of the cooktop panel. This makes it possible to achieve a level of measuring accuracy that is sufficient for the measuring operation during cooking. The measured variable used according to the invention, rather than the deformation of the cooktop panel essentially in the plane of the cooktop panel or parallel to the cooktop panel, is, thus, the displacement as a result of the deformation of the cooktop panel in a direction perpendicular to the cooktop panel. Advantageously, it is possible for the cooktop panel to be of interruption-free configuration and, thus, to be sealed against penetrating liquid.
In accordance with another feature of the invention, it is advantageous, for example, for the displacement sensor to be secured on the underside of the cooktop panel and for the actuating element to be secured on a carrier part that, in turn, is itself secured on the underside of the panel of the cooktop. Alternatively, it is also possible for the fastening locations of the displacement sensor and of the actuating element to be the other way round. Both an additional part, in particular, adhesively bonded to the underside, and a specifically formed underside of the cooktop panel are possibilities for an embodiment of the actuating element. Because the two components detecting the deformation and the resulting displacement of the cooktop panel are each fastened on the underside of the cooktop panel, disruptive influences by weight-induced loading of the work top, in which the cooktop is installed, or of the cooktop frame are ruled out.
In accordance with a further feature of the invention, to take account of the different coefficients of linear expansion between the carrier part and the cooktop panel, the carrier part is secured on the cooktop panel at least at two fastening locations, the carrier part being mounted such that it can be moved horizontally at least at one fastening location. Such mounting of the carrier part, which is free on one side parallel to the cooktop panel, rules out mechanical stressing during heating of the cooktop with its components, which stressing could be produced on account of the different thermally induced linear expansions of the cooktop panel and of the carrier part.
In accordance with an added feature of the invention, to provide the highest level of measuring sensitivity, the fastening locations of the carrier part are disposed in the border region of the cooktop panel. Such a configuration is due to the fact that these are the regions where bending of the cooktop panel is at the lowest level.
In accordance with an additional feature of the invention, there is provided a spring element applying a bias forcing the carrier part against the underside of the panel. The carrier part is forced onto the underside of the cooktop panel by at least one spring element to ensure precisely defined spacing of the carrier part relative to the cooktop panel and, thus, of the actuating element relative to the displacement sensor. In addition, in the region, the operating temperature is rather lower, which makes it easier to fasten the weighing components on the underside of the cooktop panel.
In order that the weighing configuration and the components thereof are not adversely affected in the event of overload, in accordance with yet another feature of the invention, the carrier part is mounted at one of the fastening locations such that it can be pivoted away perpendicularly from the cooktop panel.
In accordance with yet a further feature of the invention, a weighing marking is provided on the top side of the cooktop panel approximately in the center of gravity of the surface area of the cooktop panel. Such placement ensures that a user sets down the cooking vessel at the location that results in maximum deformation or bending of the cooktop panel. Alternatively, it is also possible, instead of the weighing marking, for the cooktop panel to have a raised portion in the region and to have a set-down surface projecting slightly out of the surface of the cooktop panel. If requirements for accuracy are not as stringent, however, it may also be possible for the cooking vessel to be set down on one of the conventional heating zones during the weighing operation. The extent of the bending of the cooktop panel as a result of the weight-induced loading may additionally be set by a specific reduction in the thickness of the cooktop panel at selected locations.
In order to achieve high accuracy, in accordance with yet an added feature of the invention, the displacement sensor and the actuating element are disposed approximately in the center of gravity of the surface area of the cooktop panel, in particular in the case of a weighing marking provided there.
In accordance with yet an additional feature of the invention, a reliable and precise measurement can be realized if the displacement sensor has at least one bending bar on which conventional strain gauges are disposed. To secure the bending-bar configuration in the event of overload, in accordance with again another feature of the invention, the configuration has a stop element for limiting the bending movement. The protective measure is particularly beneficial, in particular, when the carrier part is additionally mounted at one of the fastening locations such that it can be pivoted away perpendicularly from the cooktop panel.
In accordance with a concomitant feature of the invention, the cooktop panel is a glass ceramic material.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a cooktop with weighing unit, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.